Toyota charged us R2,200 more (after bargaining a discount) for essentially the same part by making our vehicle slightly differently, so that standard parts wouldn't fit.
Scroll down to the pictures to see what R2,200 extra buys you.

The Long Version:

I recently needed to replace the clutch on our '98 Toyota Land Cruiser Prado 3.0TD (3 litre turbo diesel). The engine used in the vehicle is the 1KZ-TE, which is also used in the Toyota Hilux. Overseas these vehicles are also know as the 4Runner, Hilux Surf, Land Cruiser Colorado, Land Cruiser Amazon, Hilux Pickup, etc. The newer D-4D (1KD-FTV) engine also seems to use the same clutch.

I first got a quote from Toyota on the job, which was in the region of R10,000 - with the clutch-kit costing about R6,400. I then proceeded to research clutch-kits on the internet, and get quotes from a number of aftermarket clutch-kit suppliers. The quotes were all in the region of R2,900, except for one supplier who mentioned that there were two types of clutch-kits available - with one kit costing approximately the same as the other suppliers and the other kit costing around R5,800. The difference between these two kits was that one was for vehicles which had a "4mm step in the flywheel" (the "common" and cheaper type) and the other was for vehicles with a "0.5mm step in the flywheel" (if you don't know what this means then don't worry - I didn't either at the time). From my research I determined that the Sachs kit seemed to be recommend, so I decided to purchase one of these (only one type of Sachs kit was available). I took the vehicle and clutch-kit to my local shop, who got underway with the clutch replacement.

Next, the shop called to let me know that there was a small problem with the clutch-kit I had brought. It fitted perfectly, except for one problem - the gap between the flywheel and the pressure-plate was slightly too large (once again, don't worry if you don't know what this means). I drove through to the shop to see for myself what the problem was, and they showed me that the old pressure-plate taken off the vehicle was about 3.5mm thinner than the one which came with the kit which I had bought. The quote from the supplier who had mentioned two types of clutch-kits immediately came to mind.

I took the old pressure-plate to a nearby auto-parts store in order to compare it with one from the brand of clutch-kit which they sold, and we determined that their brand's pressure-plate was also too thick.
I mentioned to the salesman there that the only difference between the two kits seemed to be the thickness of the pressure-plate, and he concurred. Asking why this might be, he explained that it was done simply to (censored) the aftermarket around. I wondered whether it would be possible to simply have an engineering shop trim 3.5mm off the pressure-plate, and also whether this was a wise idea. Did Toyota engineer in a difference in the pressure-plate simply to force people to buy over-priced parts, or was it so that people didn't accidentally install the incorrect clutch-kit for their vehicle? After getting advice from a number of sources, the consensus was that I should rather just buy the more expensive clutch-kit which was made to fit. I still however went to an engineering shop to see if they would be able to trim the pressure-plate down, but they were reluctant to do it due to the fact that it would be difficult to do this precisely - the part of the pressure plate which was thicker was riveted to the rest of the pressure-plate via springs, and the rivets would have to be removed in order to do the job properly. The other option was to try engineer a recess into the flywheel, but I decided at this point to rather just purchase the "correct" kit - the vehicle was taking up space on the shops lifts and I didn't want to waste their time any further, I was reluctant to modify the flywheel, and I had been advised to rather purchase the expensive kit.

One Toyota dealer could get the kit for me by that afternoon, and so I ordered it and drove all the way accross town to pick it up. As soon as I got there and removed the parts from the "Genuine Toyota" packaging I immediately realised that they looked fimiliar. They were, in fact, exactly the same as the parts from the clutch-kit which I had already
purchased - except that they had taken an extra 3.5mm off of the pressure-plate, like I had thought to do (they probably did this before the parts were riveted together).

I spent over a day running around, drove clean accross town, and paid an extra R2,200 (after bargaining Toyota down from R6,400 to R5,100) - not to mention travel costs, phone calls, etc - simply because of Toyota's greed. They made one part shorter and the other part longer on some vehicles, just so that aftermarket parts wouldn't fit and people would be forced to buy their exhorbitantly priced parts - which were exactly the same as the aftermarket parts, except for a slight change in the engineering process.

Below are some pictures to illustate the situation. They were unfortunately taken with a cellphone camera (at the shop which was fitting the clutch) and so the quality isn't the best, but it is still good enough that the situation is made clear.

The pressure-plates from the two different clutch-kits side-by-side - "Genuine Toyota" on the left, Sachs on the right:

The same shot as before, but from the top ("Genuine" left, Sachs right):

Below are the shots which make the "expensive" difference clear:

"Genuine Toyota":

Sachs:

Below are some shots of the clutch-plate itself, which is identical between the "Genuine Toyota" and the Sachs kits.

Side-by-side - "Genuine" left, Sachs right:

"Genuine":

Sachs:

I didn't take any pictures of the release bearing, however these are also identical between the "Genuine" and the Sachs kits.

To anybody else who finds themselves in the same situation as me, and doesn't want to purchase Toyota's exhorbitantly priced parts, I recommend the following:
It would probably be difficult to modify the pressure-plate, due to the aforementioned problems. At the least a jig would probably have to be made in order to mount it properly on a lathe. It might be possible to mill it down, however the difficulty with the springs still remains.
A better option would probably be to either cut a 3.5mm (further) recess into the flywheel, or to find a flywheel which already has the 4mm recess in it at a used-parts dealer - in which case the "common" clutch-kit can always be used in future.